The threat of light pollution puts the world’s darkest skies in the Atacama Desert at risk

ATACAMA DESERT, Chile (AP) — It takes a moment for the eyes to adjust. A faint spark appears in the darkness; then another, brighter. Soon, stars, planets and entire constellations emerge. Soon, an entire galaxy stretches across the sky, visible to the naked eye.

In Chile’s Atacama Desert, the night sky seems endless. Considered the driest place on Earth, its darkness is also one of the clearest windows onto the universe.

A rare combination of dry climate, high altitude and, above all, isolation from urban light pollution, makes the Atacama an unrivaled hub for world-class astronomy and home to the world’s largest ground-based astronomical projects.

“The conditions in the Atacama Desert are unique in the world,” said Chiara Mazzucchelli, president of the Chilean Astronomical Society. “There are over 300 clear nights a year, which means no clouds or rain. »

But the world’s darkest skies could be under threat.

Last year, the desert became a battleground between scientists and an energy company proposing a green energy complex a few miles from the Paranal Observatory. Managed by the European Southern Observatory (ESO), the site is also home to what will be the most powerful optical telescope ever built.

Although the energy project was canceled in January following a massive appeal from astronomers, physicists and Nobel laureates, it revealed deep concerns that existing sky preservation laws were lax, outdated and unclear. Since then, several environmental regulations have been revised, including one from the Chilean Ministry of Science targeting protected astronomical areas.

“We are working to ensure that the new criteria are strict enough to guarantee that there will be no impact on astronomical zones,” said Daniela González, director of the Cielos de Chile Foundation, a nonprofit founded in 2019 to protect the quality of Chile’s night skies.

The Associated Press spent three days touring the Paranal facility, in the heart of what is known as Photon Valley. In this high-altitude corridor, several observatories operate side by side using some of the most sophisticated instruments ever designed.

“Many of these large facilities are located in Chile, and the ESO telescopes in particular are the most powerful astronomical facilities on the planet,” said Itziar de Gregorio-Monsalvo, the intergovernmental organization’s representative in Chile.

Paranal is one of nearly 30 astronomical sites in northern Chile, most of which are managed by international organizations. Every year, the Atacama Desert attracts thousands of astronomers and scientists from around the world to investigate the origins of the universe.

“We are lucky to be here,” said Julia Bodensteiner, an assistant professor at the University of Amsterdam, noting that the chances of being selected as a guest astronomer at Paranal are only 20 to 30 percent.

Crossing the rocky and rugged terrain of the Atacama is no easy task. At altitudes above 3,000 meters (10,000 feet), oxygen becomes a luxury, as scorching days give way to relentlessly cold nights. But for space observation and exploration, these more than 105,000 square kilometers (40,500 square miles) of desert provide the ideal setting.

Atacama’s exceptional conditions have enabled some of the most ambitious astronomical projects ever conceived, such as the Extremely Large Telescope, ELT — a $1.5 billion ESO project scheduled for completion in 2030.

With 798 mirrors and a light-collecting area of ​​nearly 1,000 square meters (a quarter of an acre), the ELT will be 20 times more powerful than current major telescopes and 15 times more precise than NASA’s Hubble Space Telescope.

All the data compiled in these observatories play a fundamental role not only for life on Earth, but also for the possibilities of its development beyond our planet. The preservation of these research sites is essential.

With the ELT, said ESO astronomer Lucas Bordone, “we should be able to see Earth-like planets in what we call the habitable zone, so basically planets that are candidates for life.”

Twenty years ago, the Atacama Desert was “an ocean of darkness,” recalls Eduardo Unda-Sanzana, director of the Astronomy Center at the University of Antofagasta. “It was just you and the universe.”

But over the years, the landscape has changed dramatically.

Driven by urban sprawl, industrial development, the arrival of mines and wind farms, the desert has become a coveted territory where balance is not always easy to achieve.

In Paranal, specialists live like moles in an underground residence designed to keep their presence virtually undetectable. Windows should remain covered, hallways kept dark, and all outside movement should be guided only by a flashlight. Even the faintest light can interfere with telescopes.

Last year’s announcement of an imminent green energy project sent shock waves through the international scientific community. Experts have been pressuring authorities to protect Chile’s night skies from the proposed site, planned to be built just 10 kilometers (6 miles) from Paranal.

The case has raised alarm bells due to its impacts, such as increased light pollution, micro-vibrations and dust, as well as greater atmospheric turbulence. These conditions would make astronomical activities unviable.

“If you put the ELT next to a city, it doesn’t matter if its diameter is 40 meters long. It’s exactly the same as having a small telescope,” Gregorio-Monsalvo said.

Although the company canceled the project in late January, scientists warn that without new, updated regulations, similar projects could be proposed at any time.

“Despite all the hype in 2025, we find ourselves exactly where we were last year,” said Unda-Sanzana, who is also part of a ministerial advisory commission that recently made recommendations to the Chilean government following the incident.

There is no shortage of precedents. The first international heliophysics observatory in Chile – a major solar station operated by the US Smithsonian Institution in the early 20th century – was forced to close in 1955 due to environmental pollution caused by expanding mining activity in the region.

“We have had 70 years to learn from history and avoid repeating these same mistakes,” Unda-Sanzana said.

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